Method, system and paint for emi suppression

ABSTRACT

A method, system and paint for suppressing emission of high frequency electromagnetic radiation from an electronic system, the electronic system including at least one power supply unit, at least one printed circuit board (PCB) and at least one integrated circuit are provided. The method includes providing an electrically conductive housing configured to accommodate and encase the electronic system, the housing having an inner conductive surface, and applying a layer of an electromagnetic absorbing paint to the inner conductive surface of the housing to substantially cover the inner surface by the layer, the electromagnetic absorbing paint comprises a liquid matrix and an electromagnetic absorbing material.

FIELD OF THE INVENTION

The present invention generally relates to electronic equipment and,more specifically, to enclosures for electronic equipment that suppressemission of electromagnetic interference (EMI) from electronic systems.

BACKGROUND OF THE INVENTION

During normal operation, electronic equipment typically generatesundesirable electromagnetic energy that can interfere with the operationof other electronic equipment. These disturbances, known aselectromagnetic interference (EMI), are characterized by conductedemissions and radiated emissions. EMI emissions can be of a wide rangeof frequencies and may interfere with radio and wire communication. Withthe advance of computer networking and the ever increasing operatingrates of electronic systems, EMI radiation frequencies may extend intotens and even hundreds of GHz.

Electro Magnetic Compatibility (EMC) for electronic andelectro-mechanical products is mandatory in many countries. For example,in the United States, the Federal Communications Commission (FCC), whichis in charge of the regulation of radio and wire communication, setlimits on the radiated and conducted emissions of unintentionalradiator. An unintentional radiator is defined as a device that is notdesigned to produce electromagnetic waves. Nearly all digital devicesthat are not designed for RF communication nevertheless generate radiofrequency electromagnetic waves and thus can be considered unintentionalradiators.

To minimize the problems associated with EMI and to meet therequirements of electromagnetic compatibility (EMC), sources ofundesirable electromagnetic energy may be shielded and electricallygrounded. The shields may be constructed to reduce EMI at a particularwavelength, or a range of wavelengths.

EMI shields are typically constructed of a highly-conductive materialoperating to internally reflect the radiation component of the EMI andto drain the conducted component of the EMI to electrical ground. In theabstract, an ideal EMI shield would consist of a completely enclosedhousing constructed of an infinitely-conductive material without anyapertures, seams, gaps, or vents. However, in all practicalapplications, the enclosure is constructed of a finitely-conductingmaterial and has some apertures and seams that inhibit the beneficialFaraday Cage effect by forming discontinuities in the conductivity ofthe enclosure, and through which the radiation component of the EMI mayleak. Moreover, by the known Babinet principle, the apertures can act asslot antennae, resulting in the enclosure itself becoming a secondarysource of EMI. Apertures may be intentional apertures, such asventilation openings, or may be apertures inherent to the method ofconstruction such as seams between adjacent construction parts andaround connection ports. EMI shielded enclosures may also induceresonances of the electromagnetic energy within the cavity. For example,under certain conditions, reflections of the electromagnetic field atthe boundaries of the cavity can create standing waves within thecavity. Such resonances tend to increase the peak amplitudes of theelectromagnetic energy within the enclosure through additive effects ofthe multiple reflections and thus may reduce the apparent shieldingeffectiveness at the resonant frequencies.

The shielding effectiveness of an EMI enclosure having an aperture is afunction of the wavelength of the EMI. Generally, the shieldingeffectiveness is improved when the largest dimension of the aperture issmall compared to the wavelength (i.e., less than one-half thewavelength). Reducing the largest dimension of any aperture, as well asreducing the total number of apertures, tends to increase the EMIprotection or shielding effectiveness of the enclosure. Special methodsof manufacture may be employed to improve shielding effectiveness byminimizing gaps using special RF gaskets and by structurally securingdifferent parts of the enclosure to be tightly fixed to each other.

However, some apertures are unavoidable and as operating frequenciesincrease, the associated wavelengths of induced EMI decrease, leading toa reduction in shielding effectiveness for any non-ideal EMI enclosure.For frequencies and/or associated harmonies of more than 10 GHZ, thewavelengths of the EMI emission become of the same order of magnitude asthat of apertures dimensions, resulting in increase of both resonancephenomena and leakage. At such operational rates, additional means arerequired in order to suppress EMI emission from electronic equipment andto meet EMC requirements.

One known method for suppressing EMI emission from electronic equipmentis to place absorbing pads around specific components, identified assources of emission, to individually suppress each such source.Additionally, or alternatively, absorbing pads may be placed at otherlocations within the enclosure cavity, including the enclosure walls.Other known methods involve different kinds of EMI filters placed atcrucial positions inside the enclosure or the use of EMI suppressingsheets or films. However, these methods are cumbersome, labor and timeconsuming and involve large amounts of material and high costs.

There is therefore a continuous need for simple and low-cost methods andmeans for suppressing EMI emission from electronic equipment, inparticular for suppressing high frequency EMI emission at megahertzthrough gigahertz frequencies.

SUMMARY OF THE INVENTION

The present invention is aimed at providing easily implemented low-costmethods and systems for suppressing EMI emission from electronicsystems.

While reducing the present invention to practice, it was found thatapplying a thin layer of an EMI absorbing paint directly to the innersurface of a conductive enclosure of an electronic system, significantlyreduces EMI emission from the enclosure.

One aspect of the present invention is a method for suppressing emissionof high frequency electromagnetic radiation from an electronic systemthat comprises at least one circuit board (PCB), at least one powersupply, at least one integrated circuit and optionally one or more portsadapted to connect to a pluggable interconnecting means. The methodcomprises: providing an electrically conductive housing configured toaccommodate and encase the electronic system and applying a thin layerof an electromagnetic absorbing paint to the inner surface of thehousing to substantially cover said inner surface. The electromagneticabsorbing paint comprises a liquid matrix and an electromagneticabsorbing material. Preferably, the layer of the electromagneticabsorbing paint has a thickness in the range of 30 to 80 μm and covers90% or more of the housing's inner conductive surface. According to someembodiments of the invention, the electronic system produceselectromagnetic radiation at frequencies of 5 or more GHz. According tosome embodiments of the invention, the electromagnetic absorbing paintis selected to absorb electromagnetic radiation in the range of 5 to 100GHz. The electronic system may be, for example, a network switch.

According to some embodiments of the invention, the electromagneticabsorbing material comprises electrically conductive particles andferromagnetic particles homogeneously suspended in the liquid matrix.The electromagnetic absorbing material may comprise one or more ofcarbon powder, carbonyl iron powder, sendust, ferrites, iron silicide,conductive polymer, titanium oxide, silica, magnetic alloys, magneticflakes, steel wool, carbon-impregnated rubber, ferrite in a plasticstranded carrier and clad metals. According to some embodiments of theinvention, the electromagnetic absorbing paint comprises 50-80% wt. ofsaid electromagnetic absorbing material. According to some embodimentsof the invention, the liquid matrix is a polymeric liquid comprising apolymer selected from the group consisting of polyurethane, polyacrylateand silicone. For example, the liquid matrix may be a solvent-basedpolyurethane lacquer. Preferably, the liquid matrix has a low emissionof volatile organic compounds (VOC).

According to some embodiments of the invention, the housing comprises anelectrically conductive material selected from the group consisting ofcopper, aluminum, gold, tin, steel, stainless steel, nickel and anycombination thereof. According to some embodiments of the invention, thehousing comprises at least two complementary parts and the step ofproving the housing comprises providing the parts separately. Accordingto these embodiments, the step of applying the lossy paint comprisesapplying a layer of the paint to the inner surfaces of each of the partsand then assembling the housing to encase and accommodate the electronicsystem. The at least two parts may be, for example, a chassis on whichcomponents of the electronic system are mounted and a complementary lidwhich is removably connectable to the chassis, wherein the chassis andthe lid, when properly connected, substantially enclose the electronicsystem from all sides.

Another aspect of the present invention is an EMI suppressing system forsuppressing emission of high frequency electromagnetic radiation from anelectronic system that comprises at least one circuit board (PCB), atleast one power supply, at least one integrated circuit and optionallyat least one port adapted to connect to a pluggable interconnect means.The EMI suppressing system comprises an electrically conductive housingconfigured to accommodate and encase the electronic system and a layerof electromagnetic absorbing paint that substantially covers the innerconductive surface of the housing wherein electromagnetic absorbingpaint comprises a liquid matrix and an electromagnetic absorbingmaterial. According to some embodiments of the invention, the electronicsystem produces electromagnetic radiation at frequencies of 5 or moreGHz and the electromagnetic absorbing paint is selected to absorbelectromagnetic radiation in the range of 5 to 100 GHz. The electronicsystem may be, for example, a network switch.

Preferably, the housing comprises at least two complementary parts andat least one aperture. The at least two parts may be, for example, achassis on which components of the electronic system are mounted and acomplementary lid which is removably connectable to the chassis, whereinthe chassis and the lid, when properly connected, substantially enclosethe electronic system from all sides. Preferably, the housing comprisesan electrically conductive material selected from the group consistingof copper, aluminum, gold, tin, steel, stainless steel, nickel and anycombination thereof. The electromagnetic absorbing material may compriseelectrically conductive particles and ferromagnetic particleshomogeneously suspended in the liquid matrix. The electromagneticabsorbing material may comprise one or more of carbon powder, carbonyliron powder, sendust, ferrites, iron silicide, conductive polymer,titanium oxide, silica, magnetic alloys, magnetic flakes, steel wool,carbon-impregnated rubber, ferrite in a plastic stranded carrier andclad metals. Preferably, the invention, the electromagnetic absorbingpaint comprises 50-80% wt. of the electromagnetic absorbing material.According to some embodiments of the invention, the liquid matrix is apolymeric liquid comprising a polymer selected from the group consistingof polyurethane, polyacrylate and silicone. For example, the liquidmatrix may be a solvent-based polyurethane lacquer. Preferably, theliquid matrix has a low emission of volatile organic compounds (VOC).

Yet, a further object of the invention is an electromagnetic absorbingpaint comprising 20 to 40% wt. solvent-based polymer composition, 40 to70% wt. ferromagnetic particles, 5 to 15% wt. conductive polymer, 5 to15% wt. carbon black and 3 to 8% dielectric material. In someembodiments, the polymer is polyurethane, acrylic polymer, silicone or acombination thereof. The ferromagnetic particles can be carbonyl ironpowder, sendust, ferrite, iron silicide, magnetic alloy powder, magneticflakes or any combination thereof; the conductive polymer may bepoly(thiophene) (PT), poly(acetylene) (PAC), poly(p-phenylenesulfide)(PPS), poly(pyrrole) (PPY), polyaniline (PANI),poly(p-phenylenevinylene) (PPV) or a combination thereof and thedielectric material may be titanium oxide. In some embodiments, theelectromagnetic absorbing paint comprises 50-80% wt. suspended solids.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of the invention may be better understood by referring tothe following description, taken in conjunction with the accompanyingdrawings, in which:

FIGS. 1A and 1B are perspective views of an exemplary housing configuredto accommodate and encase an electronic system, in assembled anddisassembled configurations, respectively;

FIG. 2 is a perspective view of the housing of FIG. 1 having its innersurface covered by a layer of an EMI absorbing paint, in accordance withan embodiment of the present invention;

FIG. 3 is a schematic block diagram of an embodiment of the inventionshowing the main components of the electronic system;

FIG. 4 is a graph representing insertion loss as function of frequencymeasured in a microstrip test configuration for a layer of apolyurethane matrix as compared to insertion loss measured without thelayer (reference);

FIG. 5 graphically presents maximum measured radiated emissions (dBμV/m)as function of the rotation angle of the of the tested system: (a)encased in a prior art shield (reference); (b) encased in a shield withone layer of lossy paint; (c) encased in shield with two layers of lossypaint; black line represents vertical polarization, gray line representshorizontal polarization;

FIGS. 6a and 6b are an overall flow chart, and a detailed flow chart,respectively, illustrating the method of suppressing EMI from anelectronic system, in accordance with embodiments of the presentinvention.

It will be appreciated that the drawings described herein are forillustration purposes only and are not intended to limit the scope ofthe present disclosure in any way.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an EMI shield, such as ahighly-conductive metal enclosure, that is covered by a thin layer ofelectromagnetic absorbing, or lossy, paint to suppress a portion of theEMI, thereby enhancing the performance of the EMI shield over a range ofoperational frequencies. The electromagnetic absorbing paint comprises aliquid matrix and an electromagnetic absorbing material. Theelectromagnetic absorbing paint is applied directly on the conductivesurface of the enclosure, forming a direct contact between metal andpaint.

While reducing the present invention to practice, it was found that theapplication of a thin layer of an electromagnetic absorbing paintdirectly to the inner metallic surface of a conductive enclosuresignificantly attenuates emission of high frequency EMI from theenclosure. It was also found that adding a second layer of theabsorptive paint over the first layer does not significantly contributeto EMI attenuation, meaning that a thin layer of the paint is sufficientto suppress EMI emission generated by an electronic system disposed inthe enclosure's cavity. Notably, the application of the thin layer ofthe lossy paint to the inner conductive surface of the enclosureeliminates the need to separately shield individual components of thesystem. It also eliminates the need to use adhesives, or other attachingmeans, for securing the absorbing material to the enclosure walls, thus,significantly reduces material, labor and costs compared to existingmethods.

Lossy materials can be used to suppress EMI phenomena, for example, byconverting the electromagnetic energy into another form of energy, suchas thermal energy. In some embodiments, the lossy material can becomposed of ferrite-like material mixed in a polyurethane-based,acrylic-based, or silicone-based paint. In other embodiments, the lossymaterial can be composed of a lossy filler material, such as carbonpowder, carbon fiber powder and/or conductive polymers. The lossymaterials can be configured in a liquid form for coating the innersurfaces of the enclosure. Some examples of lossy materials are carbon,iron, carbonyl iron powder, sendust, ferrites, iron silicide, magneticalloys, magnetic flakes, steel wool, conductive polymers andcombinations thereof. Other materials used to achieve electromagneticsuppression effects include alumina (Al₂O₃), sapphire, silica (SiO₂),titanium dioxide (TiO₂), and combinations thereof.

Without wishing to be held to any one theory, it is currently believedthat the attenuation of the EMI by the thin layer of absorbing paint isat least partially attributable to the diffusion of the eddy currentsgenerated on the conductive surface of the internal walls into the paintlayer, which is in close contact with the metal surface and has aconsiderably lower conductance and a higher permeability, where they arereduced to heat by Ohmic and magnetic energy losses.

As used herein, the term EMI should be considered to refer toelectromagnetic radiation interference.

As used herein, the terms EMI absorbing paint, electromagnetic absorbingpaint and a lossy paint, are used interchangeably to describe acomposition that dissipates electromagnetic energy passing through itand that can be applied to a surface as paint.

As used herein, the term electronic system refers to a completefunctional system that includes at least one power supply unit, at leastone integrated circuit, at least one printed circuit board (PCB) andoptionally one or more ports adapted to connect to a pluggableinterconnecting means. The electronic system is encased in an enclosureand is a standalone functional unit. The electronic system may be anelectronic information/data system, an electronic switching system, anelectronic control system, an electronic communication system, etc.Examples of electronic systems, for which the present invention isapplicable, include computers, network switches, modems, memory units,cellular phones, etc.

In one aspect, the invention relates to an EMI suppressing system forsuppressing emission of high-frequency EMI from an electronic system.The system includes an electrically-conductive shield configured forhousing a complete functional system. The shielding system also includesan electromagnetic absorbing paint material disposed on the internalside of the electrically-conductive shield. The combinedelectrically-conductive shield and electromagnetic absorbing materialattenuate the emission of electromagnetic energy with respect to thesystem shielded by the original, not covered with the absorber,enclosure.

According to some embodiments, the electrically-conductive shield isfabricated from a highly conductive material, preferably metal, such asaluminum, copper, nickel, tin, silver, gold, beryllium, phosphor bronze,steel, stainless steel, and combinations thereof.

According to some embodiments, the energy absorptive material in thelossy paint comprises one or more of the group consisting of aconductive material, carbonyl iron powder, sendust, ferrite, ironsilicide, magnetic alloys, magnetic flakes, carbon powder, carbon fiberspowder, and a conductive polymer. The conductive polymer may be, forexample, poly(thiophene) (PT), poly(acetylene) (PAC),poly(p-phenylenesulfide) (PPS), poly(pyrrole) (PPY), polyaniline (PANI),poly(p-phenylenevinylene) (PPV), etc.

In some embodiments, the energy absorptive paint compriseselectromagnetic absorbing particles suspended in a liquid matrix. Theliquid matrix is preferably a solvent-based polymer comprising polymeror prepolymer components in a solvent. Such polymeric liquids, afterbeing applied to a surface, are cured and dried to remove the solvent,forming a polymeric layer on the surface. The polymer is preferablyselected from the group consisting of polyurethane, polyacrylate andsilicone. In some embodiment the liquid matrix is a commerciallyavailable polymeric lacquer or varnishes, also known as polymercoatings, such as commercially available polyethylene-based,silicone-based or acrylic-based coatings, for example, coatingsmanufactured by Lord Corporation, Cary, N.C., USA.

In some embodiments, the energy absorptive paint comprises one or moreof the group consisting of electrically conductive material, carbon,carbonyl iron powder, sendust, ferrites, iron silicide, conductivepolymer, magnetic alloys, magnetic flakes, steel wool,carbon-impregnated rubber, ferrite in a plastic stranded carrier, metalfoils, metal clad materials including iron, nickel, and iron/nickelcompositions, paste composites selected from the group consisting ofiron, nickel, copper with epoxy, and lacquer binders.

In some embodiments, the lossy material can be combined with othermaterials to achieve a desired effect. For example, the lossy materialcan be combined with anticorrosive agents and/or with fire retardants tomeet flammability standards.

Referring to the drawings, FIGS. 1a and 1b schematically illustrate anexemplary housing 10 configured to accommodate and substantially enclosean electronic system. Housing 10 comprises a main frame portion, orchassis, 12 and a lid 14 removably connectable to portion 12. Whenservice of components in housing 10 is needed, lid 14 can be removed toaccess the inside of the housing. Chassis 12 may be provided with one ormore internal ribs and/or protrusions 16 for receiving and supportingelectronic components of the electronic system, and with apertures 18.Apertures 18 may be air flow ventilation openings and/or portsconfigured to receive pluggable interconnect means. When assembled toencase the electronic system, housing 10 substantially encloses theelectronic system from all sides. Housing 10 comprises a highlyconductive reflecting material, preferably metal, such as copper,aluminum, gold, tin, steel and nickel. Preferably the housing isfabricated from a metal sheet. Alternatively, housing 10 may be made ofcombinations of different metals or of different conducting materials,such as steel and stainless steel, nickel-coated copper, phosphorbronze, tin plated steel, etc., or combinations of a conductive materialwith an electrical insulator, such as plastic coated with anelectrically conducting or metallic layer, as is common in the packagingof small, light-weight electronic systems. In the latter case, theconductive metal surface is oriented inwardly, i.e., constitutes theinner surface 10 i of the housing while the insulated surface isoriented outwardly and constitutes the external surface 10 e of thehousing. In all cases, inner surface 10 i of housing 10 is highlyconductive.

In accordance with the present invention, a significant portion of innersurface 10 i is covered by a layer 20 of electromagnetic absorbingpaint, as illustrated in FIGS. 2 and 3. Layer 20 is preferably 30 to 80mμ thick and substantially covers inner surfaces of both bottom (12 b,14 b) and side walls (12 s, 14 s) of parts 12 and 14. In this context,the term substantially covers should be interpreted as covering morethan about 90% of the surface area. The electromagnetic absorbing, orlossy, paint comprises electromagnetic absorbing or otherwisesuppressing material in a liquid matrix and may be applied to innersurface 10 i by spraying or brushing to form layer 20. The liquid matrixmay be a commercially available lacquer, such as polyurethane-,acrylic-, or silicone-based lacquer. After application, the sprayed, orotherwise applied, paint is cured to remove the solvent, leaving a layerof lossy paint on the metal surface.

In some embodiments, the electromagnetic absorbing material is broadbandin nature, absorbing electromagnetic energy over a broad range offrequencies, including high frequencies of up to 100 GHz and even more.Preferably, the electromagnetic material comprises high frequencyabsorbing material. According to some embodiments, the electromagneticabsorbing paint may comprise one or more of electrically conductivematerial, carbonyl iron powder, sendust, ferrite, iron silicide,magnetic alloys, magnetic flakes, carbon powder, carbon fiber powder,conductive polymer, steel wool, carbon-impregnated rubber, ferrite in aplastic stranded carrier, metal foils, metal clad materials includingiron, nickel, and iron/nickel compositions, paste composites selectedfrom the group consisting of iron, nickel, copper with epoxy, lacquerbinders.

FIG. 3 schematically illustrates an electronic system enclosed byhousing 10. In accordance with the present invention, the electronicsystem is a complete functioning system comprising at least one powersupply unit, at least one printed circuit board (PCB), at least oneintegrated circuit and optionally one or more ports adapted to connectto a pluggable interconnecting means. The power supply unit may be apower source, or a module connectable to an external power source.Preferably, the absorbing paint has a very low emission of volatileswhich is essential for avoiding contamination of the system componentsby volatiles, in particular when the system comprises optical modules,where volatiles might deposit on active optical components and hamperthe operation of these modules.

The EMI suppressing system of the invention, comprising a conductiveenclosure and a layer of lossy paint substantially covering theconductive inner surface of the enclosure, can be a newly fabricatedenclosure or the lossy paint can be added to an existing enclosure byapplying a first, high-frequency, EMI absorbing paint to a second, EMIreflecting inner surface of the enclosure. FIG. 6 outline the main stepsof the method of the invention, according to which a layer of a lossypaint is applied (step 62) to the inner conductive surface of anelectrically conducting housing (step 60). The parts constituting thehousing are provided separately (step 64) and after their inner surfacesare painted with the lossy paint (step 66) and the components of theelectronic system are mounted thereon (step 68), the housing parts areassembled to encase the electronic system within the housing (step 70).The housing is then connected to ground (step 72) to drain conductiveemissions.

EXAMPLE 1

A composition comprising carbonyl iron powder, carbon powder, titaniumdioxide and a conductive polymer in polyurethane matrix was tested in amicrostrip test setting to study the effectiveness of the composition asEMI suppressor.

FIG. 4 presents the transmission insertion loss as function of frequencymeasured in the microstrip test configuration with the testedcomposition compared to the insertion loss measured without thecomposition (reference). As can be seen, the composition attenuates theRF signal at all measured frequencies and the attenuation effectincreases with frequency. At frequencies above about 10 GHZ thecomposition attenuates radiation by more than 3 dB and above about 20GHz by 8 dB or more.

EXAMPLE 2

An electromagnetic absorbing paint was prepared by mixing solvent-basedpolyurethane coating with carbonyl iron powder, carbon black, titaniumdioxide, and polyaniline to obtain a paint of the following composition(in weight percent): n 22.4% solvent-based polyurethane, 59.2% carbonyliron, 7.2% polyaniline, 6.3% carbon powder and 4.9% TiO₂.

The EMI suppressing effect of the electromagnetic absorbing paint wasstudied on an Ethernet switch operating at 25.781 Gbps rate. TheEthernet switch was housed in an enclosure similar in structure to thehousing depicted in FIG. 1, made of 1 mm thick aluminum sheet. Testswere performed for the switch in its original enclosure (i.e., withoutpaint), with one 0.002 inch thick dry layer of the electromagneticabsorbing paint, and with two such layers of absorbing paint.

Measurements were performed in a semi-anechoic chamber that incorporatesa turntable allowing rotation of 360° and a measuring antenna. Thetested switch was placed on the turntable at a height of 1 m above theground plane, was turned on and allowed to operate normally. Thedistance between the antenna and the switch was 3 m. Radiated Emissionwas measured at a frequency of 25.781 GHz frequency. To find the highestemission, the turntable was rotated 360° and the measuring antennaheight was swept from 1 to 2 m above the ground plane and the antennawas rotated to take measurements for both horizontal and vertical planesof polarization.

FIG. 5 graphically presents the results obtained for the unpaintedhousing (reference, 3 a), for the housing with one layer of absorbingpaint (3 b) and for the housing with two layers of absorbing paint (3c). The polar graphs represent the highest radiated emission (measuredas the field strength in μV/m) as a function of the emission directionfor both vertical and horizontal polarizations.

The results clearly indicate that the paint-treated enclosure providesan improvement, or difference in attenuation, of at least about 8 dB.The results also indicate that the contribution of a second layer ofabsorbing paint is negligible.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that modifications and variations arepossible without departing from the scope of the invention. Accordingly,it will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the present invention isdefined only by the claims which follow.

1. A method for suppressing emission of high frequency electromagneticradiation from an electronic system, the electronic system comprising atleast one power supply unit, at least one printed circuit board (PCB)and at least one integrated circuit, the method comprising: providing anelectrically conductive housing configured to accommodate and encasesaid electronic system, the housing having an inner conductive surface;and applying a layer of an electromagnetic absorbing paint to the innerconductive surface of the housing to substantially cover said innersurface by said layer, said electromagnetic absorbing paint comprises aliquid matrix and an electromagnetic absorbing material.
 2. The methodaccording to claim 1, wherein the electronic system further comprises atleast one port adapted to connect to a pluggable interconnecting means.3. The method according to claim 1, wherein said layer of anelectromagnetic absorbing paint is applied to cover 90% or more of saidinner conductive surface.
 4. The method according to claim 1, whereinthe electronic system produces electromagnetic radiation at frequenciesof 5 or more GHz.
 5. The method according to claim 1, wherein saidelectromagnetic absorbing paint is selected to absorb electromagneticradiation in the range of 5 to 100 GHz.
 6. The method according to claim1, wherein said layer has a thickness in the range of 30 to 80 μm. 7.The method according to claim 1, wherein said electromagnetic absorbingmaterial comprises electrically conductive particles and ferromagneticparticles homogeneously suspended in said liquid matrix.
 8. The methodaccording to claim 1, wherein said electronic system is a networkswitch.
 9. The method according to claim 1, wherein said electromagneticabsorbing paint comprises 50-80% wt. of said electromagnetic absorbingmaterial.
 10. The method according to claim 1, wherein saidelectromagnetic absorbing material comprise one or more of carbonpowder, carbonyl iron powder, sendust, ferrites, iron silicide,conductive polymer, titanium oxide, silica, magnetic alloys, magneticflakes, steel wool, carbon-impregnated rubber, ferrite in a plasticstranded carrier and clad metals.
 11. The method according to claim 1,wherein said a liquid matrix is a polymeric liquid comprising a polymerselected from the group consisting of polyurethane, acrylic polymer andsilicone.
 12. The method according to claim 1, wherein said liquidmatrix is a solvent-based polyurethane lacquer.
 13. The method accordingto claim 1, wherein said housing comprises electrically conductivematerial selected from the group consisting of copper, aluminum, gold,tin, steel, stainless steel, nickel and any combination thereof.
 14. Themethod according to claim 1, wherein the housing comprises at least twocomplementary parts, wherein the step of proving comprises providingsaid at least two parts separately, wherein the step of applyingcomprises applying a layer of paint to the inner surfaces of each ofsaid at least two parts and wherein the method further comprisesassembling the housing to encase and accommodate the electronic systemafter the step of applying.
 15. The method according to claim 14,wherein said at least two parts comprise a chassis on which componentsof the electronic system are mounted and a complementary lid removablyconnectable to said chassis.
 16. An EMI suppressing system forsuppressing emission of high frequency electromagnetic radiation from anelectronic system, the electronic system comprising at least one circuitboard (PCB), at least one power supply, the EMI suppressing systemcomprising: an electrically conductive housing configured to accommodateand encase the electronic system, the housing comprising at least twocomplementary parts and housing having an inner conductive surface; anda layer of electromagnetic absorbing paint substantially covering theinner surface of the housing, wherein said electromagnetic absorbingpaint comprises a liquid matrix and an electromagnetic absorbingmaterial.
 17. The EMI suppressing system of claim 16, wherein theelectronic system further comprises at least one port adapted to connectto a pluggable interconnecting means.
 18. The EMI suppressing system ofclaim 16, wherein said layer of an electromagnetic absorbing paintcovers 90% or more of said inner conductive surface.
 19. The EMIsuppressing system of claim 16, wherein the electronic system produceselectromagnetic radiation at frequencies of 5 or more GHz and whereinsaid electromagnetic absorbing paint is selected to absorbelectromagnetic radiation in the range of 5 to 100 GHz.
 20. The EMIsuppressing system of claim 16, wherein said layer is 30 to 80 μm thick.21. The EMI suppressing system of claim 16, wherein said electronicsystem is a network switch.
 22. The EMI suppressing system of claim 16,wherein said electromagnetic absorbing material comprise one or more ofcarbon powder, carbonyl iron powder, sendust, ferrites, iron silicide,conductive polymer, titanium oxide, silica, magnetic alloys, magneticflakes, steel wool, carbon-impregnated rubber, ferrite in a plasticstranded carrier and clad metals.
 23. The EMI suppressing system ofclaim 16, wherein said a liquid matrix is a polymeric liquid comprisinga polymer selected from the group consisting of polyurethane,polyacrylate and silicone.
 24. The EMI suppressing system of claim 16,wherein said housing comprises an electrically conductive materialselected from the group consisting of copper, aluminum, gold, tin,steel, stainless steel, nickel and any combination thereof.